1. Field of the Invention
The present invention relates generally to a variable capacity swash plate type compressor, and more particularly relates to a hinge means for pivotally and inclinably supporting a swash plate of a variable capacity swash plate type compressor suitable for use in an air conditioning system of an automobile.
2. Description of the Related Art
Conventional variable capacity swash plate type compressors are disclosed in U.S. Pat. No. 4,073,603 granted to Abendschein et al. and in Japanese Unexamined Utility Model Publication (Kokai) No. 1-114988. For example, the latter compressor is provided with a hinge unit shown in FIG. 4, in which a rotor 91 is fixed to a drive shaft 90 disposed in a crank chamber, and a long hole 91a is formed in the rotor 91. As best shown in FIG. 5, the long hole 91a of the rotor 91 is parallel with a plane determined by the central axis "y" of the drive shaft 90, and the top dead center of a rotary swash plate 93, and the long hole 91a extends toward the central axis "y" of the drive shaft 90 from the radially outside of the drive shaft so that an inner end of the long hole 91a is located adjacent to the central axis "y" of the drive shaft. The opposite ends of a section of the long hole 91a taken perpendicularly to the center line "S" thereof extends linearly so as to be parallel with a plane perpendicular to the axis of rotation of the drive shaft 90. A connecting pin 92 is slidably inserted into the long hole 91a of the rotor 91, and has an outer end thereof connected with the rotary swash plate 93 via a bracket 93a of the rotary swash plate 93, so that the rotary swash plate 93 can be inclined back and forth. A non-rotating wobble plate (not shown) is slidably mounted on the rotary swash plate 93, and a piston rod is provided between the wobble plate and each piston accommodated in each of a plurality of cylinder bores formed in a cylinder block of the compressor.
In the described conventional compressor, the rotation of the drive shaft 90 is converted into the rotation of the rotary swash plate 93 and the wobbling motion of the wobble plate by the action of the hinge unit "K". The wobbling motion of the wobble plate is converted into the reciprocating motion of each piston. In this case, pressure in the crank case chamber is controlled by a control valve (not shown in the drawing). Therefore, the inclination angle of the wobble plate is changed, so that the stroke of each piston is also changed. Accordingly, the discharge capacity of the compressor is changed. At this time, the back and forth tilting motion of the rotary swash plate 93 and the nutating motion of the wobble plate are restricted by the long hole 91a having a predetermined radius of curvature. Accordingly, although the inclination angle of the rotary swash plate 93 is changed, the top dead center of the wobble plate is unchanged in the back and forth direction, resulting in the top clearance of each piston in the corresponding cylinder bore becoming approximately zero at the top dead center of the piston.
However, in the above described type of compressor, since a suction force acts on the piston during the suction stroke thereof, the suction force also acts on the rotary swash plate 93 in a region from the top dead center to the trailing side thereof with respect to the direction of rotation of the drive shaft 90 (i.e., approximately the right half portion of the swash plate 93 in FIG. 4). On the other hand, since a compression-reaction force acts on the piston during the compression stroke thereof, the compression-reaction force also acts on the rotary swash plate 93 in a region thereof extending from the top dead center to the preceding side with respect to a direction of rotation of the drive shaft 90, i.e., approximately the left half portion of the swash plate 93 of FIG. 4. To this end, in the above-described compressor, the trailing side of the swash plate 93 with respect to the direction of rotation of the drive shaft 90 is separated away from the rotor 91, and the preceding side of the swash plate 93 with respect to the direction of rotation of the drive shaft 90 is pressed against the rotor 91.
In the compressors disclosed in the Unexamined Utility Model Publication (Kokai) No. 1-114988, the rotary swash plate 93 is mounted on the drive shaft 90 via a cylindrical sleeve (not shown in FIGS. 4 and 5), and the cylindrical sleeve supports the rotary swash plate 93 via trunnion pins so as to slide in a direction parallel with the central axis "y" of the drive shaft 90 and to nutate back and forth. Accordingly, the rotary swash plate 93 is prevented from conducting uncontrolled twisting motion in a direction different from the nutating direction with respect to the rotor 91 even when the suction force and compression-reaction force act on the rotary swash plate 93.
Nevertheless, in order to permit the rotary swash plate 93 to smoothly perform the nutating motion back and forth, a small gap must be provided between the cylindrical sleeve and the drive shaft 90. Thus, the rotary swash plate 93 is slightly twisted by the above-described suction and compression-reaction forces in a direction different from the back and forth direction with respect to the rotor 91 (for example, the rotary swash plate 93 is twisted by an angle ".alpha.", and the connecting pin 92 comes into contact with the long hole 91a in a point contact condition at a point "I" in FIGS. 4 and 5. Therefore, the suction and compression-reaction forces are concentrically received at the point "I".
Further, when an input torque is exerted by the drive shaft 90, the torque is transmitted from the rotor 90 to the rotary swash plate 93 via the hinge unit "K". Therefore, when the rotary swash plate 93 is constantly twisted by a small angle in the direction different from the exact back and forth direction with respect to the rotor 91, the torque must be concentrically sustained at the point I.
Accordingly, in the conventional compressor, the hinge unit "K" provided for regulating the back and forth tilting motion of the swash plate 93 is subjected to an abnormal abrasion during the high speed operation thereof and during the high compression ratio operation thereof.
Similar problems are encountered in a case where, from the viewpoint of easy manufacture of the internal mechanism of the compressor, a sleeve element having a spherical supporting surface is slidably mounted on a drive shaft so as to support a back and forth nutating motion and a rotating motion of the rotary swash plate, respectively, and a pair of equal hinge units are disposed at positions on both sides of the top dead center of the rotary swash plate.
In addition, by suitably adjusting an arrangement of the hinge unit, the amount of a clearance "TC" defined at the top dead center of each piston changes along a curve having an upwardly convexed curvature during the change in an angle of inclination of the swash plate from the minimum inclination angle position to the maximum inclination angle position. Thus, for example, as shown by a curve "A" in FIG. 6, when the clearance TC at the top dead center of each piston is set at an optimum amount at the time when the swash plate takes the minimum inclination angle position, the amount of clearance "TC" unfavorably increases at the time when the swash plate takes the maximum inclination angle position. Otherwise, as shown by a curve "B" in FIG. 6, when the clearance TC at the top dead center of each piston is set at an optimum amount at the time when the swash plate takes the maximum inclination angle position, the amount of clearance "TC" unfavorably increases at the time when the swash plate takes the minimum inclination angle position. Namely, since the amount of clearance "TC" at the top dead center of the pistons changes by a large amount, a sufficient volumetric efficiency of the compressor cannot be obtained.